In order for non-woven fabrics to have textile qualities, they must have two basic properties: strength, and soft hand. These two properties are usually mutually exclusive as a result of the characteristics of non-woven production processes. For instance in the production of non-woven fabrics ultrasonically, such as disclosed in U.S. Pat. No. 4,259,399, high bonding density to create acceptable strength usually results in degradation of the softness of the hand; and conversely, low bonding density yields soft hand but weak fabrics.
One proposal to produce a non-woven fabric ultrasonically having both good strength properties and soft hand is to provide reinforcement with a secondary scrim, which is a sheet of yarn relatively open in construction both in the machine direction and the cross-machine direction. However there are great difficulties in practicing this technique, and if the reinforcing scrims are not actually bonded at the bonding points, delamination takes place easily. If actual bonding takes place between the web and the scrim, the bond points are usually thermally degraded to the extent that very minimal bond strength still remains.
According to the present invention a method is provided for bonding reinforcing yarns to a web, during ultrasonic production of non-woven fabric, without inadvertently destroying the strength of the reinforcing yarns. This is accomplished by introducing reinforcing yarns formed of bi-component fibers in the warp direction prior to the passage of a batt of primarily ultrasonically fusible fibers into operative association with a plurality of ultrasonic vibration sources and anvil means cooperating with the vibration sources. The term "reinforcing yarn of bicomponent fibers" as used in the present specification and claims means: yarns having fibers wherein one component is a strong filament fiber, and provides reinforcement to an ultimate non-woven fabric being formed, and has a relatively high melting point; while the other component of the fiber has a relatively low melting point. The yarns may be either spun from staple fibers, or continuous filament yarns.
A non-woven fabric also is provided according to the present invention. The non-woven fabric produced includes a layer of strong filament reinforcing yarns integrated into the body of the non-woven fabric. This provides an increase in the strength of the non-woven fabric without delamination of the components and without degradation of the component yarns. The reinforcing yarn is formed of bi-component fibers. The production of the non-woven fabric according to the present invention is accomplished utilizing a plurality of ultrasonic vibration sources and anvil means, and feeding the batt--with reinforcing yarns laid on top of it--into operative association with the vibration sources and anvil means.
It is the primary object of the present invention to provide a non-woven fabric having good strength and hand properties, and an ultrasonic method of production thereof. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.